CB Conversion to 10-Meter AM

[WB0NUM]

Hello,

I have recently aquired a Teaberry "T" Control CB that has been Screw-Drived almost into oblivion. Is there anyone out there that has a copy of Sam's Photofact CB-88 Manual that is looking to sell the manual? I have already gotten the schematics from Secret CB, but this site does not provide the alignment instructions found in the Sam's. Looks like a GREAT canidate for 10-Meter AM. The schematics from Secret CB appear to require changing the 11MHZ crystal to a little bit higher frequency to shift the radio where I wish to operate.

Any help would be GREATLY APPRECIATED! This is a VERY HARD manual to get my hands on.

-73's-

Jon  WB0NUM

Contact: jonsperberg@yahoo.com

[w5rkl]

Jon,

I have never converted a Teaberry "T" 11 meter transceiver to 10 meter AM. I have converted a Johnson Messenger One and Messenger 223 to 10 meter AM, 223 is VFO control (N3ZI DDS VFO) both on 29.0Mhz on 10 meter AM.

I read the Teaberry T manual pages on transmit and receive synthesizer mixing and came up with the following:

To receive 29.0Mhz the synthesizer output frequency is "40.275Mhz". To make the synthesizer produce that signal you do not change the 11.275Mhz crystal, you change the 14Mhz crystals.

Here's an example of the mixing process for 29.0Mhz and 29.010Mhz receive and transmit using 10Khz channel spacing:

Change the channel One crystal from 14.950Mhzl to 16.985Mhz:

16.985 + 23.290 = 40.275Mhz

The receive signal, 29.0Mhz, mixes with the 40.275Mhz synthesizer signal producing the "difference" mixer output frequency of "11.275Mhz" (40.275 - 29.0 = 11.275), the first IF amplifier frequency that is applied to the first IF amp.

The transmit mixing is just as easy to calculate:

16.985 + 23.290 = 40.275 - 11.275 = 29.0Mhz transmit

Change channel two 14.960Mhz crystal to 16.995Mhz and use the same mixing math for receive and transmit which will put the receiver on 29.010Mhz and transmit on 29.010Mhz. Use the transceiver's service manual and schematic, all the information is there.

I don't recommend spacing the channels closer than 10Khz.

Alignment is very easy, receive being the easiest. You adjust the appropriate coils/transformers for peak output. L915 is a "TVI" adjustment, you don't need to adjust L915, leave it alone.

The signal generator should be adjusted for less than 1mv output applied to the receiver during receive alignment.

Change the crystals, peak the synthesizer output signal, then adjust the receiver followed by the transmitter.

Again, I have not converted a Teabarry T so I'm basing my comments on the schematic, how the synthesizer produces the mixer input signal, and the basic receive and transmit circuit. It's not difficult. I would start with one crystal, 16.985Mhz, International Crystals in Oklahoma City, OK, can make one for you for $22 plus a buck or two shipping via USPS. Takes about 2 weeks.

Just my 2 cents worth.


73
Mike W5RKL

[w5rkl]

You can use the Teaberry T Charlie One 13.6VDC transceiver alignment instructions, found on CB Tricks, to align the 120VAC power transceiver.

I did a quick review of the 2 schematics and they both appear to be the same except for the power supplies, one is 120VAC only while the other is for 13.6VDC only.

Converting a 11 meter transceiver to 10 meter AM is fun.

Operating 10 meter AM on low power is a challenge but it also is a lot of fun. I have work both coast with my converted 5 and 7 watt Johnson Messenger 223 and Messenger One transceivers with only a simply 10 meter inverted vee up 25 feet. The Messenger 223 uses a non-amplified D-104 microphone and the Messenger One uses the original factory hand microphone. Have fun.

73
Mike W5RKL

[KD6VXI]

Look for a digi scan.   Gives digital readout and the entire 10 meter band in 5khz  steps.

--Shane
KD6VXI

[K9PNP]

Maybe this will help.  Shows xtal mixing scheme in most of the rigs made.

http://www.cbcintl.com/XTALS/xtals.htm

[w5rkl]

Maybe this will help.  Shows xtal mixing scheme in most of the rigs made.

http://www.cbcintl.com/XTALS/xtals.htm

I could be wrong but I have to disagree with the conversion cbcintl.com is showing for receive in the Teaberry T and Charlie 1, there is a conversion step that is missing. The transmit mixing is correct.

If one follows the receive mixing process, "A + B - D", then the first mixer input would be "23.290 + 14.950 - 11.730 = 26.510Mhz which won't work.

The first receive mixer must has an output frequency of 11.275Mhz which can only be achieved by mixing the 40.235Mhz synthesizer output with the RS (Receive Signal). The following receive mixing scheme example assumes the 14.950Mhz crystal is changed to 16.985Mhz for receiving 29.0Mhz 10 meter AM.

The synthesizer output for channel 1 is 40.235Mhz (23.290 + 16.985 = 40.235).

The 40.235Mhz signal is then applied to the first mixer along with the 29.0Mhz receive signal resulting in a first mixer output "difference" frequency of 11.275Mhz (40.235 - 29.0 = 11.275). This is the missing step the mixing scheme shown in cbcintl.com file.

At this point the 11.275Mhz first mixer output frequency is then mixed with the receive second oscillator, 11.730Mhz, in the second receive mixer, producing a "difference" frequency of 455Khz which is the second IF frequency (11.730 - 11.275 = .455).

Transmitting a 29.0Mhz signal uses the same 40.275Mhz synthesizer output frequency that is mixed with the 11.275Mhz transmit oscillator in the second transmit mixer, producing a "difference" frequency of "29.0Mhz" (23.250 + 16.985 - 11.275 = 29.0) which is the actual TC (Transmit Carrier) signal (A + B - C = TC).

I might find a Teaberry T or Charlie One transceiver and purchase a 16.985Mhz crystal from International Crystal and modify either transceiver to see if this all works.

73
Mike W5RKL